How do Fluorescence work?
A fluorophore absorbs photons at an excitation wavelength, moves to an excited electronic state, loses some energy by non-radiative relaxation, and then emits photons at a longer wavelength when it returns to the ground state. The difference between excitation and emission maxima is the Stokes shift. A fluorescence spectrometer consists of an excitation source such as a xenon arc lamp, laser or LED, excitation and emission monochromators or filters, a sample holder for cuvettes, microplates or flow cells, and a detector such as a photomultiplier tube, avalanche photodiode or CCD. Because the detector is positioned at 90 degrees to the excitation beam, transmitted light is largely excluded and sensitivity can be orders of magnitude higher than absorption methods. Signal intensity depends on quantum yield, concentration, path length and quenching by oxygen, pH or matrix components.
Which Fluorescence variants are available?
- Benchtop Fluorescence Spectrophotometer — A benchtop fluorescence spectrophotometer records excitation and emission spectra of cuvette samples.
- Microplate Fluorescence Reader — A microplate fluorescence reader measures fluorescence from samples in 96, 384 or 1536 well plates.
- Time-Resolved Fluorescence Lifetime Spectrometer — A time-resolved fluorescence lifetime spectrometer measures how long a fluorophore stays in the excited state after a short light pulse.
- HPLC Fluorescence Detector — An HPLC fluorescence detector measures the fluorescence of analytes as they elute from a liquid chromatograph.
- Field Fluorometer for Water Quality — A field fluorometer measures fluorescence of dyes, chlorophyll or dissolved organic matter directly in water samples or streams.
How do I choose the right variant?
Select a fluorescence system by the sample format and the sensitivity required. Cuvette-based spectrofluorometers are best for method development and identity work because both excitation and emission wavelengths can be scanned. Microplate readers are the choice for high-throughput screening and enzyme assays in 96, 384 or 1536 wells. Time-resolved instruments measure fluorescence lifetimes and reject short-lived background for assays with long-lived labels. HPLC fluorescence detectors add selective quantitation to chromatographic separations. Portable filter fluorometers serve field water and tracer measurements where wavelength coverage matters less than speed. Compare excitation and emission ranges, stray-light rejection, detector type, minimum detectable concentration and software features such as spectral correction and blank subtraction.
Where are Fluorescence used?
Fluorescence are specified in pharmaceutical assay and impurity testing, nucleic acid and protein quantitation with fluorescent dyes, water quality monitoring of algae, chlorophyll and fluorescent tracers, food and beverage vitamin, mycotoxin and adulteration analysis, clinical immunoassays and labeled biomarker detection and environmental and hydrology tracer studies.
Which standards and certifications apply?
Work with Fluorescence is commonly governed by USP <853> Fluorescence Spectroscopy, ASTM E579 Standard Practice for Limit of Detection of Fluorescence, ICH Q2(R2) Validation of analytical procedures, ISO/IEC 17025 and IEC 61010-1. Instrument certifications such as CE marking are confirmed per configuration and never assumed.
What are the key considerations before purchase?
Install fluorescence instruments away from bright daylight and strong UV sources because stray light raises background. Xenon lamps produce ozone and heat and need adequate ventilation and lamp-hour tracking. Verify wavelength accuracy with reference standards and check sensitivity using the water Raman band or quinine sulfate in dilute sulfuric acid. Fluorescence is highly sensitive to dissolved oxygen, pH, temperature and quenching agents, so control and record these factors. Avoid photobleaching by limiting exposure of strongly fluorescent samples. Clean cuvettes and microplates must be free of fluorescent contaminants, and instrument qualification should follow IEC 61010-1 for safety and internal quality procedures for performance.
